Examples of zero insertion force (ZIF) test sockets have been used in industry for many years. The requirement for zero insertion force arose to prevent damage to IC leads from the wiping action as the lead is forcefully inserted into socket contacts. Herein, IC is defined to include DIP, SIP and power hybrid in-line packages, e.g. T0-220 and similar such types. Burn-in is defined as monitored electrical operation of the IC, under elevated ambient temperature for a period of time, to screen out quality defective devices. This process is routinely done on virtually all ICs produced, and therefore automation of the process is desirable. Typical existing sockets have cam or other such mechanical actuators which deflect the socket contacts to allow an integrated circuit (IC) to be inserted without the IC leads wiping the contacts. The cam is then rotated to a closed position and the mechanical linkages provide the force to make electrical contact between the IC leads and the socket contacts. These linkages are unreliable, especially under the environmental extremes of high temperature IC burn-in.
To reduce IC costs, manufacturers plate the IC leads thinner (down to 4 microns) with such alloys as nickel-palladium. The plating is not rugged, and, thus, it is even more important to prevent damage to the IC leads.
Typically, the electrical connections between the test/burn-in socket contacts and the IC leads are made on that part of the IC lead which is soldered to a printed circuit board (PCB) in production assembly of the IC and, so, may damage the IC lead.
Some existing test/burn-in sockets will mechanically guide the IC leads with protrusions to place the IC in proper position for making electrical contact to the IC leads. These protrusions may damage the IC leads by stubbing and/or deflecting them. Thus, automated use of this socket requires precise registration between the loading device and the test socket.
Burn-in sockets for IC packages usually have flat blanked, stamped out contacts which are individually installed into the socket housing. In some such sockets the contacts are not within the same plane such that gang-mounting of connected contacts is precluded. Such an arrangement requires manual loading of each contact. These limitations have prevented the wide spread automation of assembly of test/burn-in sockets and their use.
The fact that some sockets have flat blanked, non-coplanar contacts also precludes automated selective plating; thus each contact must be plated all over with a precious metal such as gold.
Some existing test/burn-in sockets require contacts to have two or more tail configurations, in order to separate adjacent tails on the PCB, which must have a solder pad for each tail.
In test/burn-in sockets used with power ICs, the socket contacts must be heavy to accommodate the higher currents (up to several amps and more). These heavy contacts are stiff requiring high forces to open, and such contacts can only be forced open a short distance in order not to exceed the yield strength of the contact materials and permanently deform the contacts.
Another limitation of existing test/burn-in socket contacts is that they connect to one or both of the flat sides of an IC lead and require the socket contacts to be narrow enough to avoid shorting adjacent IC leads while still making reliable contact with the IC leads. One approach to solve this problem is to use the narrow edge of a flat stamped contact, but such an edge incurs sharp edges and other non-smooth surfaces which may damage the IC lead plating. The alignment must also be carefully controlled in such sockets. Another limitation of existing test/burn-in sockets is that their contacts are encased in slots of the dielectric housing material, thus restricting air flow over the contacts and impeding heat dissipation.
It is an object of this invention to improve reliability by reducing the mechanical linkages in ZIF test/burn-in sockets.
It is another object of this invention is to provide a test/burn-in socket wherein the IC leads are not contacted on that part of the IC lead which is soldered to a PCB.
It is a further object of this invention to provide for a test/burn-in socket wherein the IC leads are substantially untouched throughout a test/burn-in cycle including associated handling through drop-in mounting of the IC into the test socket with no mechanical guiding of the IC leads, and then to make electrical connections after such mounting.
It is an object of this invention to lower the cost of the socket by facilitating the use of selective gold plating.
It is still another object of this invention to provide improved registration between the IC leads and the socket contacts.
It is still a further object of this invention to improve assembly and to lower the cost of the socket by using only one contact tail configuration.
It is another object of the present invention to provide socket contacts which can be opened wide while allowing the high current required by power ICs, and wherein the wide opening also serves to improve the automatic loader positioning tolerance.
Another object of the present invention is to provide test contacts that require less accurate registration, and also a smoother contact surface.
It is an object of this invention to provide a socket with minimal encasement of its contacts in dielectric so as to maximize air circulation and thermal dissipation to enhance high current performance.